Compact rotationally steerable ultrasound transducer

ABSTRACT

According to the present invention, an ultrasonic probe for use with a remote ultrasonic imaging system is provided, having a multielement transducer with an upper surface and a lower surface. An ultrasonically attenuative backing material adjoins the lower surface of the multielement transducer. The attenuative backing material is disposed within a container. A circular track is mounted to the container, and a flexible assembly and a carrier band are attached to the container. The carrier band may be operable to rotate the multielement transducer about an axis defined by the circular track. Alternatively, the circular track may be operable to rotate the multielement transducer. Additionally, a method of forming near real-time images of an object in a plane that is oblique to the axis of rotation of the multielement transducer is provided.

This application is a continuation of application Ser. No. 08/479.617,filed Jun. 7, 1995 now U.S. Pat. No. 5,575,288 which is continuation ofapplication Ser. No. 08/069,092, filed on May 28, 1993, now U.S. Pat.No. 5,465,724.

BACKGROUND OF THE INVENTION

The invention relates to ultrasonic imaging systems, and moreparticularly to systems that utilize a transducer probe to sendultrasonic signals to a remote ultrasonic imaging system.

The users of medical ultrasound transducer probes, hereinafter referredto as sonographers, can access bodily regions to be imaged via theirfree hand physical manipulation, rotation, sliding and tilting of thetransducer probe. One area in particular where this manipulation is morechallenging is transesophageal cardiac imaging. During transesophagealcardiac imaging, the sonographer orients a scanhead at the tip of thetransducer probe in the esophagus or stomach of a patient in order toobtain different fields of view of the heart. To obtain the desiredviews of the heart, the sonographer may have to slide, twist or curl thetransducer probe in order to properly position the scanhead, whichcontains the imaging transducer(s).

For this application, it has been found desirable to rotate thetransducer contained in the scanhead independently from the scanheaditself. In combination with the ability to slide, twist or curl thescanhead, the ability to independently rotate the transducer(s) whilethe scanhead is stationary gives the sonographer the ability to obtainan ultrasonic image of any image plane orthogonal to and intersectingthe face of the transducer(s) at each location to which the scanhead canbe moved. By giving the sonographer the ability to remotely rotationallyorient the acoustic device in the scanhead to obtain different imageslices of the heart or its valves, for example, patient comfort isincreased. Further, the time required for an ultrasonic examination maybe reduced.

Devices are known that incorporate a remotely rotationally adjustabletransducer. For example, U.S. Pat. No. 4,543,960 to Harui et al.discloses a transesophageal echo cardiography scanhead. The elements ofthe transducer are mounted upon a rotatable base, which is connected bya shaft to a pulley below the transducer. A-control cable is directedinto the scanhead and is attached to the pulley. The elements of thetransducer are electrically connected to a wire bundle by flexible PCBinterconnects. The control cable is guided, through a pair of guidetubes, out of the scanhead so that the operator can control the angularrelationship of the transducer with respect to the housing.

A disadvantage of the Harui device is that the pulley, shaft andflexible PCB interconnects require a considerable volume within thescanhead. It is desirable to maintain a minimum profile scanhead so thatthe scanhead may be easily inserted into the body and manipulatedtherein without causing excessive patient discomfort.

A further disadvantage of the Harui device is that, during rotation ofthe transducer, bending and axial stresses act upon the flexible PCBinterconnects. In addition, the striking of the inner wall of thescanhead by the flexible PCB interconnects during rotation may cause theinterconnects to buckle, jam and/or abrade. Because these devicesgenerally cannot be repaired on site if broken and can cause majordisruptions for their users and subjects if they fail while inserted ina patient, it is desirable to maximize the reliability of such rotatableprobe devices. Additionally, with the device described, the flexible PCBinterconnects may not act efficiently as thermal conductors. It isdesirable to conduct heat away from the transducer(s) during itsoperation to avoid a "hot spot" on the scanhead in the lens area abovethe transducer, which could produce patient discomfort.

Another device incorporating a remotely rotationally adjustabletransducer is disclosed in U.S. Pat. No. 5,176,142 to Mason. Masondescribes using a rotating cable to drive a gear train within a scanheadof a probe. The gear train rotates a shaft-mounted transducer supportstructure. The transducer array is linked to conductors connected to theremote imaging electronics by a flex cable assembly. A first portion ofthe flex cable assembly is embedded in an acoustic damping material,which fills the volume within the support structure. The flex cableassembly protrudes out of the damping material, through an opening inthe support structure, and extends around the support structure in theform of a loop. The loop portion of the flex cable assembly becomesstraight and extends into a rear volume within the scanhead. In the rearvolume, the flex cable assembly is formed into a spiral, which iswrapped around and attached to a stationary post.

A disadvantage of the Mason device is that the flex cable assembly issubjected to bending and axial stresses as the transducer array isrotated by the gear train, and the flex cable assembly may buckle, jamand/or abrade as it is ejected into or pulled from the rear volume.Additionally, the flex cable assembly and the shaft present acousticdiscontinuities within the acoustic damping material. It is desirable tominimize acoustic discontinuities in the damping material and tominimize the worst bending excursion, axial buckling potential andabrasion experienced by any portion of the flex cable assembly. Further,the Mason device contains a complex gear train that occupies substantialspace within the scanhead and may produce particulate debris that mayinterfere with the operation of the device.

Accordingly, it would be desirable to have an improved remotelyrotationally-steerable medical ultrasound transducer device.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an ultrasonicprobe for use with a remote ultrasonic imaging system is providedcomprising a multielement transducer having an upper surface and a lowersurface, an ultrasonically attenuative backing material adjoining thelower surface of the multielement transducer, a container having a walland a bottom, the attenuative backing material being disposed within thecontainer, a track connected to the container, a flexible assemblyattached to the container, and a carrier band attached to the container.The carrier band is operable to rotate the container about an axisdefined by the track.

According to a second aspect of the present invention, a compactrotationally steerable ultrasound transducer for use with a remoteultrasonic imaging system and a gastroscope is provided comprising amultielement transducer having an upper surface and a lower surface, anultrasonically attenuative backing material adjoining the lower surfaceof the multielement transducer, a container having a cylindrical walland a bottom, the attenuative backing material being disposed within thecontainer, a flexible assembly having at least two layers wherein one ofthe layers is a carrier band, each of the layers being connected to thecylindrical wall of the container, and a circular track mounted to thecontainer. The circular track is operable to rotate the multielementtransducer.

According to a third aspect of the present invention, a method offorming a near real-time ultrasonic image of at least a portion of asurface that intersects in at most one point an axis of rotation of aremotely rotatable ultrasonic multielement transducer is provided,comprising the steps of slewing the ultrasonic multielement transducerabout the axis of rotation to a plurality of angular positions, scanninga selected scan line within the surface at each angular position, anddisplaying the selected scan line scanned at each angular position, thedisplayed scan lines forming the image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a first preferred embodiment of a compactrotationally steerable medical ultrasound transducer probe.

FIG. 2 is a top sectional view of the first preferred embodiment of acompact rotationally steerable medical ultrasound transducer scanhead.

FIG. 3 is a sectional view of the embodiment of FIG. 2.

FIG. 4 is a radial section of a circular track in the scanhead of FIG.3.

FIG. 5 is a second preferred embodiment of the circular track shown inFIG. 4.

FIG. 6 is a third preferred embodiment of the circular track shown inFIG. 4.

FIG. 7 is a fourth preferred embodiment of the circular track shown inFIG. 4.

FIG. 8 is a fifth preferred embodiment of the circular track shown inFIG. 4.

FIG. 9 is a perspective view of a portion of the circular track shown inFIG. 8.

FIG. 10 is a sixth preferred embodiment of the circular track shown inFIGS. 8 and 9.

FIG. 11 is a seventh preferred embodiment of the circular track shown inFIGS. 8 and 9.

FIG. 12 is a cutaway perspective view of a presently preferredembodiment of a compact rotationally steerable medical ultrasonictransducer scanhead.

FIG. 13 is a sectional view of the acoustic device shown in the scanheadof FIG. 12.

FIG. 14 is a perspective view of the acoustic device shown in FIG. 13.

FIG. 15 is an alternative embodiment for the acoustic device shown inFIG. 13.

FIG. 16 is a sectional view of a presently preferred embodiment of thecompact rotationally steerable medical ultrasound transducer having twocorotatable multielement transducers.

FIG. 17 is a sectional view of a presently preferred embodiment having amagnetic position sensor co-rotatable with the multielement transducer.

FIG. 18 is a perspective view of a compact rotationally steerablemedical ultrasound transducer probe scanhead and an oblique image planethat is scanned according to a presently preferred method.

FIG. 19 is a sectional view of the probe scanhead according to apresently preferred embodiment wherein the flexible assembly forms tworolling loop regions.

FIG. 20 is a cutaway perspective view of the acoustic device and therolling loop regions of FIG. 19.

FIG. 20A is a cutaway perspective view of an alternative construction ofthe acoustic device shown in FIGS. 19 and 20.

FIG. 21 is a sectional view of the scanhead probe showing an alternativearrangement of the flexible assembly shown in FIG. 19.

FIG. 22 is a top sectional view of the scanhead probe shown in FIG. 21.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows a transesophageal echocardiography probe 20 in accordancewith the invention. The probe 20 has a control housing 22 upon which oneor more control knobs 24 are mounted. A gastroscope 26 extends from thecontrol housing 22. An ultrasonic scanhead 28 having a window 30 islocated at a distal end of the gastroscope 26. The control housing 22 isconnected to a remote ultrasound system 32 (not shown) by a cable 34.

FIG. 2 is an enlarged section of the ultrasonic scanhead 28 shown inFIG. 1. The scanhead 28 has a housing 36 with a cavity 38 formedtherein. The cavity 38 contains an acoustic device 40 and a flexibleassembly 42. A carrier band 120 is laminated to or cofabricated with theflexible assembly 42. At one end, the flexible assembly 42 and thecarrier band 120 are attached to the circumference of the acousticdevice 40 at a location 44. Slack in the flexible assembly 42 is storedin a region 46 of the scanhead cavity 38. The other end of the flexibleassembly 42 is electrically connected to a wire bundle (not shown)extending from the gastroscope 26.

The acoustic device 40 is capable of being rotated about an axis 48. Asthe acoustic device 40 rotates in the direction of arrow 50, theflexible assembly 42 and the carrier band 120 are drawn from the region46 and co-wrapped around the outer diameter of the acoustic device 40.Phantom outline 52 illustrates the position of the flexible assembly 42and the carrier band 120 in region 46 after the acoustic device 40 isrotated approximately 180 degrees. The location 44 at which the flexibleassembly 42 is attached to the acoustic device 40 is shown in phantomafter this rotation at location 54.

A portion of the flexible assembly 42 and colaminated carrier band 120remains stationary during rotation of the acoustic device 40. Apermanent 180 degree bend 56 is formed in the flexible assembly 42 andthe carrier band 120. Preferably, the bend 56 is rigidly encapsulated,for example in an epoxy, to insure that it does not flex duringoperation of the device 40. Alternatively, the bend 56 may slightlydeform in an elastic manner during operation. A stationary length 58 ofthe flexible assembly 42 extends from the bend 56 toward the gastroscope26 (not shown). The permanent 180 degree bend 56 and the stationarylength 58 are preferably anchored to the scanhead housing 36. Theportion of the flexible assembly 42 extending from the start of the 180degree bend 56 toward the gastroscope 26, including the stationarylength 58, is hereinafter referred to as the stationary portion of theflexible assembly 42.

The remainder of the flexible assembly 42 may be referred to as themovable portion of the flexible assembly 42. When arranged as shown inFIG. 2, the carrier band 120 moves in unison with the movable portion ofthe flexible assembly 42. On the movable portion of the flexibleassembly 42, the carrier band 120 is shown laminated to the side of theflexible assembly 42 that is nearest the walls of the scanhead housing36.

As shown in FIG. 2, the flexible assembly 42 may be fabricated from twolayers of flexible circuitry 41, 43. Typically, one of the layers of theflexible circuitry 41, 43 has a plurality of flex interconnect traces82, shown in FIG. 3, formed thereon or therein, and the other layer is adielectric insulating layer such as 5 to 35 micron thick polyimide,Parylene™ or Kapton™ film. Other adhesive and cover layers (not shown)may also be utilized.

Ultraminiature flat cables suitable for this application are availablefrom Tayco Engineering Incorporated of Cypress, Calif.

The flex interconnect traces 82 may be fabricated using conventionalthin-film, thick-film or additive/subtractive plating process techniqueswhile the flexible assembly 42 and carrier band 120 are in a flat state.Typically, the interconnect traces 82 are thin, metallic,fatigue-resistant and lithographically formed interconnects made fromgold, copper or alloys thereof. The optimal thickness of theinterconnect traces 82 is approximately 5 to 35 microns.

The traces 82 preferably have a net compressive stress as formed in theflat state. The net compressive stress insures that for all points alongthe length of the flex interconnect traces 82 contained in the movableportion of the flexible assembly 42, the flex interconnect traces 82remain in a compressive state regardless of the position of the movableportion of the flexible assembly 42. The carrier band 120, if laminatedto the face of the flexible assembly 42 that is convex on the movableportion of the flexible assembly 42, will also tend to insure thepreferred compressive stress states in the flex interconnect traces 82.

FIG. 3 is a side view of the ultrasonic scanhead 28 shown in FIG. 2. Theacoustic device 40 has a multielement transducer 60 mounted on a base62. The base 62 comprises a container 64 that is filled with anultrasonically attenuative backing material 66. The container 64 of theacoustic device 40 is mounted on a ring-shaped circular track 68. Thecircular track 68 is supported by the scanhead housing 36.

A generally flat (shown) or slightly domed (not shown) window 30 isfixed in the scanhead housing 36 above the acoustic device 40.Ultrasound waves may pass in either direction through the window 30. Theinterface 70 between the window 30 and the housing 36 is sealed toprevent the ingress of damaging disinfectants and sterilizing agents aswell as the potential incubation of pathogens.

A cylindrical acoustic lens 72 is attached to the multielementtransducer 60. The acoustic lens 72, which may be fabricated of arubbery material such as RTV silicone, provides elevational focussing tothe ultrasound beam. A plurality of electronic time delays associatedwith the remote ultrasound system 32 (not shown) provide azimuthal beamsteering. In the embodiment shown in FIG. 3, the acoustic lens is fixedto and rotates with the multielement transducer 60. Alternatively, thelens 72 may be incorporated into the window 30 that is fixed in thescanhead housing 36, wherein the lens would then be generallyhemispherical or domed in shape. As a second alternative, themultielement transducer 60 may be a concave elevationally curved arrayof piezoelements, such that the multielement transducer is focussed inthe elevation plane without an acoustic lens. The concave curved array,like the multielement transducer 60 with the lens 72, may be azimuthallyfocussed using electronic time delays.

A material 74 fills the volume between the rotatable acoustic device 40and lens 72, and the fixed window 30. The material 74 conforms to thelens 72 and the window 30. Preferably, the material 74 comprises anacoustic liquid 76 (not shown) and a secondary filler 78 (not shown),wherein the secondary filler 78 is saturable with the acoustic liquid76, has significant elastomeric properties, and does not significantlydegrade the acoustic properties of the acoustic liquid 76. An example ofan acceptable secondary filler 78 is a synthetic hydrophilic polyvinylalcohol (PVA) permeable flexible membrane, as sold by Kanebo PVAMaterials of Elmhurst, Illinois. The deformable secondary filler 78inhibits undesirable liquid currents, which may distort the ultrasoundbeam.

The secondary filler 78 may be rigidly held along its circumference, bya clamping ring 80, to the rotating acoustic device 40. As analternative to the secondary filler 78 and acoustic liquid 76, thematerial 74 may be an appropriate liquid, gel or paste of sufficientviscosity to avoid thermally or rotationally induced currents that maydisrupt image quality.

In FIG. 3, a cutaway view of the flexible assembly 42 is shown so thatboth the stationary portion 56, 58 and the movable portion may be seen.Again, phantom outline 52 illustrates the position of the flexibleassembly 42 and the carrier band 120 in region 46 after the acousticdevice 40 is rotated approximately 180 degrees about the axis 48. Theflexible assembly 42 carries and routes the flex interconnect traces 82between the rotating acoustic device 40 and the wire bundle (not shown)extending from the gastroscope 26.

At the distal end of the flexible assembly 42, the flex interconnecttraces 82 are connected to mating electrically conductive traces 84 onor within the container 64 of the acoustic device 40. Preferably thecontainer 64 is fabricated from a thermally conductive ceramic, such asaluminum nitride, silicon carbide or beryllium oxide, so that the traces84 may be formed upon or within the container 64 using conventionalthick-film or thin-film technology. At the proximal end of the flexibleassembly 42, the flex interconnect traces 82 are connected to electricalconductors (not shown) that are routed through the gastroscope 26 to theremote ultrasound system 32.

Because of the mechanical protection and stability provided by thecarrier band 120 to the flexible assembly 42, and provided by thecontainer 64, a high density of interconnection between the flexinterconnect traces 82 and the electrically conductive traces 84 on thecontainer 64 can be reliably achieved. Consequently, a flexible assembly42 that is shorter along the axis 48, or a greater number ofelectrically independent elements 130, shown in FIG. 14, may beutilized. High density tape automated bonding ("TAB") or tight-pitchsoldering/welding methods are preferably utilized to electricallyconnect the flex interconnect traces 82 to the conductive traces 84 onthe container 64.

Preferably, the joints between the flex interconnect traces 82 and thetraces 84 are strain relieved by bonding the carrier band 120 to thecontainer 64. By having the carrier band 120 wrap around the container64 beyond the trace 82/trace 84 joints, a region is provided to rigidlybond the carrier band 120 to the circumference of the container 64 aswell as to provide a thermally conductive joint for the heat to passfrom the container 64 into the carrier band 120.

The carrier band 120 is preferably constructed of a thin elasticallybendable material, such as a thin silver alloy or copper alloy bandhaving a thickness of approximately 0.0007 to 0.0100 inches. As analternative, the carrier band 120 may be fabricated from thin, flexibleceramic or glass. The material should have a high yield strength andexcellent fatigue resistance such that all operational deformations areelastic in nature, no mechanical fatigue takes place, and the carrierband 120 is very resistant to localized bending on a small radius, asmay otherwise occur in an undesired local buckling event.

If the carrier band 120 is to function as a heat sink, it is preferablyfabricated from beryllium copper or silver copper, which are thermallyconductive. Alternative thermally conductive materials include silver orcopper plated stainless steel or titanium. As another alternative, thethermal conductivity of the carrier band 120 may be greatly increased bycoating the carrier band 120 with a thin-film vapor-deposited orplasma-deposited diamond layer. The carrier band 120 will radiate heatinto the gas or liquid filled scanhead housing 36 or transfer heatdirectly to the scanhead housing 36 in the region where the carrier band120 is attached to the scanhead housing 36. By providing an increasedheat sinking path, the carrier band 120 allows the acoustic device 40 tobe operated at increased acoustic power levels without exceeding theprobe's thermal limit. Accordingly, image quality and imagingpenetration are improved.

The carrier band 120 may be utilized for electrical functions inaddition to its mechanical and/or thermal functions. For example, thecarrier band 120 may function as a common electrical ground return or asa common electrical hot lead for the multielement transducer 60.Further, the carrier band 120 may function as an electrical groundreference plane to control the impedance of the flex interconnect traces82.

FIGS. 4 through 11 show some of the possible configurations for thecircular track 68 shown in FIG. 3. One function of the circular track 68is to provide rotational guidance for the acoustic device 40 and theflexible assembly 42. More particularly, the circular track 68 ensuresthat the acoustic device 40 rotates only about the axis 48 defined bythe circular track 68 so that the rotational driving mechanism employeddoes not have to overcome binding and jamming of the rotating acousticdevice 40. Further, the circular track 68 provides rotational guidancewithout using an axial shaft, which would disrupt the acoustic integrityof the attenuative backing material 66. A simple circular track 68 thatprovides rotational guidance may be formed by placing a raised circularlip about the axis 48 on the floor of the scanhead housing 36. A matingcircular groove or ridge would be provided on the bottom of thecontainer 64. Additional functions that the circular track 68 mayperform include driving of the rotational motion, clamping and fasteningthe acoustic device 40 to prevent undesired motions along the axis 48,and braking or clutch functions.

FIG. 4 shows a radial section of one embodiment of the circular track68. In this embodiment, the circular track 68 comprises a ring-shapedroller or ball bearing. The acoustic device 40 is attached to a rotatingring 86, which rotates about the axis 48. A stationary ring 88 is fixedto the scanhead housing 36. Ball bearings 90 are located between thestationary ring 88 and the rotating ring 86. Cylindrical or taperedcylindrical rollers may be used in place of ball bearings 90. Retainersor other devices customarily used to hold bearing components togetherare not shown in the Figures.

FIG. 5 shows a radial section of an embodiment of the circular track 68that is similar to the ring-shaped roller or ball bearing shown in FIG.4. The acoustic device 40 is attached to an inner rotating ring 92,which rotates about the axis 48. An outer stationary ring 94 is centeredabout and coaxial with the axis 48 and fixed to the scanhead housing 36.Ball bearings 90 are located between the outer stationary ring 94 andthe inner rotating ring 92.

FIGS. 6 and 7 show embodiments of the circular track 68 that are similarto the embodiments shown in FIGS. 4 and 5 respectively. The ballbearings 90, however, are replaced with a lubricating layer 96, such asa polytetrafluoroethylene film, that allows relative nonbinding slidingmotion of the rings 86 and 88 or 92 and 94. The lubricating layer 96 maybe a free standing film or may be a coating on one or both of the matingsurfaces of the rings 86 and 88 or 92 and 94. The embodiments of thecircular track 68 shown in FIGS. 6 and 7 guide the acoustic device 40 inrotational motion about the axis 48.

The embodiments of FIGS. 4 through 7 provide rotational guidance to theacoustic device 40, as well as fixing the three dimensional position ofthe acoustic device 40, in very compact dimensions. In the embodimentsshown, the rotating ring 86 or inner rotating ring 92 may be integratedinto the container 64 of the acoustic device 40. Similarly, thestationary ring 88 or outer stationary ring 94 may be integrated intothe scanhead housing 36. Additionally, an extremely low profileair-supported bearing could be formed by replacing the ball bearings 90in FIGS. 4 and 5 or the lubricating layer 96 in FIGS. 6 and 7 with athin film of externally sourced compressed air, which is exhaustedthrough the gastroscope 26. A plurality of air channels may be formed inthe mating rings of the air-supported bearing.

FIGS. 8 and 9 show an embodiment of the circular track 68 that iscapable of driving the rotation of the acoustic device 40 in addition toproviding rotational guidance. In FIG. 8, a radial section about theaxis 48 of the acoustic device 40 and the scanhead housing 36 is shown.A preferably reentrant groove 98 is formed in the surface 104 of thescanhead housing 36. The reentrant groove 98 is circular in shape and iscentered about the axis 48. At least one pin or peg 100 is slidablymounted in the groove 98. Each pin or peg 100 interlocks with a matinghole 102 or similar abutting edge feature, such as a ledge, formed inthe bottom of the rotatable acoustic device 40.

FIG. 9 shows a sliding chain or wire 106 to which several of the pins orpegs 100 are firmly attached. This assembly may be placed in thecircular reentrant groove 98, shown in FIG. 8, in the surface 104 of thescanhead housing 36. The chain or wire 106 may be a woven orsingle-strand polymeric, glass, ceramic or metal fiber, cord, band, wireor multi-link miniature chain. As an example, a KEVLAR™ fiber or bandcould be utilized.

FIG. 10 shows an alternative embodiment of the circular track 68 that iscapable of driving the rotation of the acoustic device 40 in addition toproviding rotational guidance. The acoustic device 40 is attached to atoothed ring 108, the toothed ring 108 being centered about the axis 48.The toothed ring 108 engages a toothed worm gear 110, which is driven bya torsional control cable 112. In addition, the toothed ring 108 may beprovided with a groove or bearing surface (not shown) to rotate in oraround so that the toothed ring 108 may be kept centered about the axis48. Alternatives to the worm gear shown in FIG. 10 include a bevel gear,hypoid gear or a spur gear.

In FIG. 11, another embodiment of the circular track 68 is shown. Thisembodiment is capable of driving the rotation of the acoustic device 40and of providing rotational guidance. In addition, this embodiment iscapable of providing rotational position sensing.

FIG. 11 shows the acoustic device 40 attached to a rotor ring 114. Astator ring 116 is positioned below the rotor ring 114 and is fixed tothe scanhead housing 36. The rotor ring 114 and the stator ring 116 arecentered about the axis 48. The rotor ring 114 and the stator ring 116together comprise a piezomotor capable of piezoelectrically driving andguiding the acoustic device 40. In the expanded view of the interfacebetween the rotor ring 114 and the stator ring 116, a travelling sinewave 118 is shown.

As will be recognized by those skilled in the art, the torsional drivingforce is derived from piezoelectrically created traveling sine waves inthe interface between the rotor ring 114 and the stator ring 116.

Piezomotors, such as that formed by rings 114 and 116, can be verysmall, can achieve continuous rotation as well as stepping rotation,have intrinsically high torque at all speeds, and act as brakes when notenergized. Further, piezomotors do not require the use of a centralmotor shaft. The ring shaped piezomotor 114/116 as shown is preferred,although the piezomotor may alternatively be disc shaped. Where thepiezomotor is used to drive the rotation of the acoustic device, the useof rotational control cables passing from the control housing 22, shownin FIG. 1, into the scanhead housing 36 is eliminated. Finally, arotational position sensor may be incorporated into the piezomotor asdescribed in S. Segawa et al., Ultrasonic Piezomotor Equipped with aPiezoelectric Rotary Encoder, IEEE Ultrasonics Symposium 1205-09 (1990).

FIG. 12 shows a sectioned perspective view of a rotatable acousticdevice 40 according to the present invention. The acoustic device 40, aspreviously described in relation to FIG. 2, has a multielementtransducer 60 mounted on a base 62. The base 62 is a container 64 thatis filled with an attenuative backing material 66. Electrical traces 84are formed on the external surface of the container 64. A generally flatwindow 30, or a hemispherical or domed combination lens/window 30, isfixed in the scanhead housing 36 above the acoustic device 40. Thehemispherical lens/window 30 provides elevational focussing for anyrotational position of the acoustic device 40.

The acoustic device 40 is attached to the embodiment of the circulartrack 68 shown in FIGS. 8 and 9. As shown in FIG. 12, the pegs 100,which are connected to the sliding band 106, project from the reentrantgroove 98 formed in the surface 104 of the scanhead housing 36. Each peg100 interlocks with a mating hole 102 in the container 64 of theacoustic device 40. The acoustic device 40 may rest directly upon thesliding band 106 and/or the pegs 100. Alternatively, the acoustic device40 may rest on the surface 104 and be dragged in rotation by the pegs100.

The container 64 may be formed of two pieces. A first circular pieceforming the bottom and a second cylindrical piece forming the sides ofthe container 64. This allows the circular bottom piece to be fabricatedwith materials, coatings and features that optimize the mechanicalmating and tribological considerations of the sliding band 106/peg100/surface 104 to container 64 interface.

FIG. 12 also shows the flexible assembly 42, having flex interconnecttraces 82, described above with reference to FIGS. 2 and 3. In theembodiment of FIG. 12, the flex interconnect traces 82 are disposed onone or both (shown) faces of the flexible assembly 42. Further, thecarrier band 120 is co-wrapped with the flexible assembly 42 around theacoustic device 40, but, in this embodiment, is not laminated orotherwise attached to the flexible assembly 42. The carrier band 120 andthe flexible assembly 42 are attached to the circumference of theacoustic device 40 such that the flexible assembly 42 is positionedbetween the carrier band 120 and the container 64. In this manner, thecarrier band 120 protects the flexible assembly 42 from abrasive damage.

The flexible assembly 42 is otherwise disposed within the scanheadcavity 38 as shown in FIGS. 2 and 3. In particular, the flexibleassembly 42 has a stationary portion, including the 180 degree bend 56,where the flexible assembly 42 reverses direction to provide the flexinterconnect traces to the back of the scanhead housing 36 and thegastroscope 26, shown in FIG. 1. The carrier band 120 may also containtermination hardware (not shown), which allows mating of the carrierband 120 to a control cable or wire 142, as shown in FIGS. 16 and 17,extending from the gastroscope 26 into the scanhead housing 36. Thetermination hardware may prevent the carrier band 120 from distorting inan undesirable manner, in the region where the control cable or wire 142is connected to the carrier band 120, when the control cable or wire 142pulls upon the carrier band 120. Although both the carrier band 120 andthe circular track 68 shown in FIG. 12 are capable of driving therotation of the acoustic device 40, only one driving mechanism isneeded.

FIGS. 13 and 14 show how the acoustic device 40 of the preferredembodiment is constructed. In FIG. 13, the acoustic device 40 ispositioned below the window 30 that is fixed in the scanhead housing 36.The material 74, described above in reference to FIG. 3, separates therotatable acoustic device 40 from the window 30. In the embodiment shownin FIGS. 13 and 14, the lens 72, shown in FIG. 3, is incorporated intothe window 30. The axis 48 about which the acoustic device 40 rotates isshown for reference only.

FIG. 13 shows the attenuative backing material 66 located within thecylindrical container 64. At least one electrically conductive groundelectrode 122 passes through the interface between the attenuativebacking material 66 and the inner wall of the container 64 and acrossthe upper surface of the attenuative backing material 66. Themultielement transducer 60 is positioned within the cylindricalcontainer 64 on top of the ground electrode 122 that passes across theupper surface of the attenuative backing material 66, such that thearray 60 is generally flush with the top edge of the cylindricalcontainer 64.

FIGS. 13 and 14 show the electrically conductive traces 84 that havebeen formed on the outer surface of the container 64 as discussed abovewith respect to FIG. 3 and as shown in FIGS. 3 and 12. Preferably, theconductive traces 84 pass over the top edge of the cylindrical container64 as shown in FIG. 13.

A metal film layer 124 interconnects the electrically conductive traces84 and the multielement transducer 60. An epoxy or other filler materialmay provide a smooth physical bridge 126 between the inner wall of thecontainer 64 and the multielement transducer 60. The multielementtransducer 60 may have a metalization layer (not shown) on its uppersurface to facilitate electrical connection between the multielementtransducer 60 and the metal film layer 124. An insulating layer 128overlies metal film layer 124. The layer 128 may be KAPTON™ with themetal film layer 124 formed upon it using known processing techniques.Additionally, the insulating layer 128 may be of a thickness andacoustic impedance such that it serves as an acoustic matching layer.Alternatively, an acoustic matching layer may be provided on top of theinsulating layer 128, or the metal film layer 124 may be formed directlyupon the multielement transducer 60 in which case the insulating layer128 serves only as an acoustic matching layer.

In one preferred embodiment, the metal film layer 124 and the insulatinglayer 128 are cofabricated independently as a flexible circuit having atleast one thin polymer material serving as the insulating layer 128 anda patterned metalization layer serving as the metal film layer 124.KAPTON™, UPILEX ™ or MYLAR™, with or without an added adhesive film, maybe utilized to fabricate the polymer material. The metalization layermay be nickel, gold or gold-plated copper. The adhesive layer, ifutilized, may be used between the insulating layer 128 and the metalfilm layer 124 as is known in the manufacture of flexible circuitry,although the adhesiveless bilayer construction shown in FIG. 13 ispreferable acoustically.

Alternatively, the metal film layer 124 may be formed by directlydepositing a metalization layer on top of the multielement transducer60, the top edge of the container 64 and the bridge 126 using anelectroplating, electroless plating, vapor-deposition or other thin-filmor thick-film deposition process. Deposition masking may be utilized toprotect the electrically conductive traces 84 on the outer surface ofthe container 64 or, alternatively, the metal film comprising the traces84 may be deposited with the metal film layer 124 without using adeposition mask. After the metal film layer 124 is deposited, it may bepatterned as required using known lithographic or laser techniques. Ifthe metal film comprising the electrically conductive traces 84 isdeposited with the metal film layer 124, the same patterning techniquesmay be used to pattern the electrically conductive traces 84 as are usedto pattern the metal film layer 124.

FIG. 14 is a perspective view of the acoustic device shown in FIG. 13.The multielement transducer 60 has a number of electrically independentelements 130 separated by dicing kerfs 132 formed by dicing an initiallycontiguous piezoelectric material. If the metal film layer 124 is formedby directly depositing a metalization layer on the top of the initiallycontiguous piezoelectric material, the top edge of the container 64, andthe filler material 126, then the metal film layer 124 may, as analternative, be patterned by appropriate dicing after the metalizationis deposited. In particular, the surface of the acoustic device 40 maybe diced so that each electrically conductive trace 84 on the outersurface of the container 64 is aligned with and electrically connectedto only one of the electrically independent elements 130. Although thephysical bridge 126 between the inner wall of the container 64 and themultielement transducer 60 is shown in FIG. 14 for clarity, it would notbe visible through the metal film layer 124.

The dicing kerfs 132, as shown in FIG. 14, extend through the wall ofcontainer 64 and are cut to a depth 136. The depth 136 must be greatenough to form the electrically independent elements 130. Accordingly,as shown in outline in FIG. 13, the dicing kerfs 132 extend below thedepth of the ground electrode 122. In this manner, the acoustic elements130, along with their electrodes, the metal film layer 124 and theground electrode 122, are acoustically and electrically isolated fromeach other, as is required.

As an alternative to the initially contiguous piezoelectric material,the multielement transducer 60 may be fabricated from a compositeconstruction of piezoelectric elements and a polymeric filler material.Dicing of the composite material is not necessarily required and theacoustic elements 130 may be electrically isolated by appropriatepatterning of the metal film layer 124.

FIG. 15 shows an alternative arrangement to the arrangement of thecontainer 64, attenuative backing material 66 and multielementtransducer 60 shown in FIGS. 13 and 14. In the embodiment of FIG. 15,the multielement transducer 60 is laminated to the electricallyconductive traces 84 on the top edges of the cylindrical container 64. Aground electrode 122 is connected to the top surface of the array 60.Preferably, the multielement transducer 60 has a thin film metalizationlayer on its top and bottom surfaces so that the ground electrode 122and the electrically conductive traces 84 may be connected to the thinfilm metalization at the edge of the array 60.

An advantage of the approach of FIG. 15 is that the depth of the dicingkerf 132 projecting into the container 64 is substantially reduced incomparison to the depth of the dicing kerf 132 projecting into thecontainer 64 as shown in FIGS. 13 and 14. Because of the fragility ofthe edges of the container 64, it is desirable to minimize the depth ofthe dicing kerf 132 projecting into the container 64. In addition, whenusing the construction of FIG. 15, it is not necessary to have anelectrode, such as ground electrode 122 shown in FIG. 13, pass along theinner wall of the container 64. A disadvantage of the embodiment shownin FIG. 15 is that undesirable acoustic coupling between themultielement transducer 60 and the container 64 will be greater becauseof the direct bond between them.

A compromise between the arrangements of FIGS. 13 and 15 may be used inwhich the outer edge of the multielement transducer 60 is generallycoincident with the inner wall of container 64, as shown in FIG. 13, butthe bottom surface of the multielement transducer 60 is generallyaligned with the top edge of container 64, as shown in FIG. 15. Thisembodiment of the acoustic device 40 alleviates the acoustic couplingbetween the multielement transducer 60 and the container 64.

As described with reference to FIGS. 13 through 15, the electricallyconductive traces 84 are electrically connected to the electricallyindependent elements 130 of the multielement transducer 60, eitherdirectly or through metal film layer 124. The electrical connection toeach electrically independent element 130 of the multielement transducer60 enables each element 130 to be selectively pulsed or placed in areceive mode.

The operation of the preferred embodiments will now be described ingreater detail. Referring to FIG. 1, a transesophageal echocardiographyprobe 20 in accordance with the present invention is shown. The controlhousing 22 of the probe 20 contains the mechanical means for bending thetip region of the gastroscope 26 to effect good acoustical contactbetween the anatomy of interest and the ultrasonic scanhead 28.Typically, the control housing 22 will have one control knob 24 for eachplane in which the tip of the gastroscope 26 may be manipulated.Typically, the gastroscope 26 would contain at least one tensioned guidewire or control cable (not shown) for each control knob 24 in order totransmit the bending forces by selective manipulation of the guidewiretensions in the tip region via the control knob(s) 24. Also containedwithin the probe 20 are the electrical connections between theultrasonic scanhead 28 and the remote ultrasound system 32 andmechanical connections between the ultrasonic scanhead 28 and thecontrol housing 22.

The electrical connections transmit power from the ultrasound system tothe acoustic device 40 and transmit electrical signals produced by themultielement transducer 60 to the ultrasound system. In addition, theelectrical connections may transmit temperature indicating and/orpositional signals or data. As shown in FIGS. 2, 3 and 12, the flexinterconnect traces 82 within or upon the flexible assembly 42 carry theelectrical signals within the cavity 38 of the scanhead housing 36. Theflex inter-connect traces 82 are connected to mating electricallyconductive traces 84 formed upon or within the container 64.

For a transesophageal echocardiography device, one desires amultielement transducer that is capable of 180 degrees of unrestrictedrotational motion. To achieve this, the flexible assembly 42 should bedesigned so that in the wound up state virtually all of the movableportion of the flexible assembly 42 is wrapped around the acousticdevice 40 and there is minimal to no excess movable portion of theflexible assembly 42 residing in region 46 of the scanhead housing 36.In this manner, the amount of the flexible assembly 42 to be unwoundduring rotation of the acoustic device 40 through 180 degrees amounts toa length of approximately one-half of the circumference of the acousticdevice 40. For clarity, the flexible assembly 42 shown in FIGS. 2 and 3exaggerates the lineal length necessary for 180 degree rotation and fullunwinding.

Mechanical connections between the ultrasonic scanhead 28 and thecontrol housing 22 may be utilized to rotate the acoustic device 40.Referring again to FIGS. 2 through 12, several preferred arrangements ofthe carrier band 120, the flexible assembly 42 and the circular track 68are described for driving rotation of the acoustic device 40. In a firstpreferred arrangement, the circular track 68 drives rotation of theacoustic device 40 and, as shown in FIG. 2, the carrier band 120 islaminated to or formed integrally with the flexible assembly 42, thecarrier band 120/flexible assembly 42 being co-wrapped around theacoustic device 40. In a second preferred arrangement, the circulartrack 68 drives rotation of the acoustic device 40 and, as shown in FIG.12, the carrier band 120 is co-wrapped with the flexible assembly 42around the acoustic device 40 but is not laminated to or formedintegrally with the flexible assembly 42. Alternative constructions forthe circular track 68 that are capable of driving rotation of theacoustic device 40 have been described with reference to FIGS. 8 through11.

Referring again to FIG. 12, the operation of the first and secondpreferred arrangements of a remotely rotationally steerable medicaltransducer, wherein the circular track 68 drives rotation of theacoustic device 40 in addition to providing rotational guidance, will bedescribed. The peg and chain embodiment of the circular track 68 will bedescribed, although the alternative constructions of the circular track68, shown in FIGS. 10 and 11, could also be used to drive rotation ofthe acoustic device 40.

The circular track 68 includes a reentrant groove 98 located in thesurface 104 of the scanhead housing 36. A sliding band 106 having pegs100 attached thereto is positioned within the groove 98. As discussedwith respect to FIG. 12, each peg 100 interlocks with a mating hole 102in the bottom of the container 64 of the acoustic device 40. The band106 may be fabricated from KEVLAR™ polymer, of circular or rectangularcross-section, having the pegs 100 fused to it or molded to it directly.

The inside of the reentrant groove 98 may be lubricated by a disposedlubricant, by surface treatments, or by the use of a self-lubricatingmaterial from which the groove 98 is formed, molded or machined. Thereentrant groove 98 may be fabricated of machined sapphire, a commonlyused high quality bearing material. This provides the sliding band 106with a slippery and wear-resisting groove 98 in which to slide.

A control wire or cable 142 (not shown) extends into the scanheadhousing 36 from the gastroscope 26 and is attached to one end of thesliding band 106. The reentrant groove 98 will diverge from a trulycircular shape in the region where the control wire 142 is connected tothe band 106. Preferably, the groove 98 is formed such that it directsthe band 106 downwards and away from the bottom side of the acousticdevice 40 at the region where the band 106 and the reentrant groove 98diverge from the truly circular shape. Laser or ultrasonic machining ofsapphire may be utilized to form the regions of the reentrant groove 98wherein the sliding band 106 and the groove 98 are directed away fromthe bottom of the container 64. By forming the groove 98 to direct theband 106 downward, abrasion between the band 106, pegs 100 and thebottom of the container 64 can be avoided.

A driving force applied in a direction 139 to the sliding band 106 isexerted by the control cable or wire 142. As the driving force isapplied to the sliding band 106, the band 106 slides within the groove98 causing the acoustic device 40 to rotate in a clockwise directionabout the axis 48. The driving force is preferably generated by a linearpiezomotor located in the control housing 22, where the linearpiezomotor is attached to the control wire 142. The linear piezomotor iscapable of producing very smooth motions and is able to accurately stepor index the rotational motion of the acoustic device 40 so thataccurately located image planes may be obtained. The linear piezomotormay also be adjusted to account for any stretching or compression of thecontrol wire 142. A suitable commercially available linear piezomotorfor this application is the INCHWORM™ linear piezomotor manufactured byBurleigh Instruments, Inc. of Fishers, New York. Alternatively, theforce driving rotation may be generated by a linear actuator.

A sliding band 106 without pins or pegs 100 may alternatively be used torotate the acoustic device 40. In this driving arrangement, the acousticdevice 40 rests directly on the portion of the sliding band 106 thatmoves in true circular motion. An axial bias spring may be utilized tocreate a mechanical downward preload on the acoustic device 40 pressingit against the sliding band 106 to provide enough friction such that theband 106, or the band 106 and peg 100 system, may drag or carry theacoustic device 40 without slip-page.

In the case where a single control wire is connected to one end of thesliding band 106, a torsional spring (not shown) under or around theacoustic device 40 may be used to torsionally preload the acousticdevice 40 so that the control cable 142 works against the spring'sresistance. Alternatively, two control wires may extend into thescanhead housing 36 through the gastroscope 26, each being attached toan opposite end of the sliding band 106 to drive rotation in eitherdirection. The carrier band 120 ensures that the largest radius ofcurvature that can be formed by the movable portion of the flexibleassembly 42, at each degree of winding or unwinding, will be maintained.

In a third preferred arrangement, the carrier band 120 drives rotationof the acoustic device 40, while the circular track 68 passively guidesrotation about the axis 48. The carrier band 120 of the third preferredarrangement is co-wrapped with the flexible assembly 42 around theacoustic device 40, but is not laminated to the flexible assembly 42, asshown in FIG. 12. In this arrangement, the driving force 138, shown inFIG. 12, is supported by the carrier band 120 and not the flexibleassembly 42. Alternative constructions for the circular track 68 thatare capable of passively guiding the acoustic device 40 in rotationabout the axis 48 have been described with reference to FIGS. 4 through7.

Referring again to FIG. 12, the operation of the third preferredarrangement of a remotely rotationally steerable medical transducer,wherein the carrier band 120 drives rotation of the acoustic device 40,will be described. As shown in FIG. 12, the acoustic device 40 ismounted on the circular track 68. The peg and chain embodiment of thecircular track 68, described with reference to FIGS. 8 and 9, isillustrated, although the alternative constructions shown in FIGS. 4through 7 are preferred for the arrangement wherein the carrier band 120drives rotation. The carrier band 120 is co-wrapped with the flexibleassembly 42 around the acoustic device 40. The carrier band 120 is not,however, laminated or attached to the flexible assembly 42 in the region46 of the scanhead housing 36. The carrier band 120 is connected to asliding control cable or wire 142 (not shown), which passes through thegastroscope 26 in a guidetube (not shown) to the control housing 22. Atorsional spring (not shown) under or around the acoustic device 40 maybe used to torsionally preload the acoustic device 40 so that thecontrol cable 142 works against the spring's resistance. The sonographermay manipulate the control cable 142, using the linear piezomotor orlinear actuator in the control housing 22, to exert a driving force inthe direction 138 on the carrier band 120, thereby causing the acousticdevice to rotate counter-clockwise about the axis 48. Where, as here,the carrier band 120 is used to drive rotation of the acoustic device40, the circular track 68 acts passively to fix rotation about the axis48.

As the sliding control cable pulls the carrier band 120, causing theacoustic device 40 to rotate in the counter-clockwise direction in theembodiment shown, the torsional spring (not shown) winds and the movableportion of the flexible assembly 42 and the carrier band 120 unwrap fromthe acoustic device 40 in a controlled manner. By directing the drivingforce to rotate the acoustic device 40 through the carrier band 120 andby positioning the carrier band 120 between the flexible assembly 42 andthe wall 140 of the scanhead housing 36, the flexible assembly 42 andthe flex interconnect traces 82 thereon will be unwrapped from theacoustic device 40 in a manner that protects the flexible assembly 42and the traces 82 from abrasion, buckling and rubbing against thesurfaces of the scanhead housing 36, as well as from any substantialaxial loading. As the driving force in the direction 138 on the carrierband 120 is released, the flexible assembly 42 and the carrier band 120are rewound about the acoustic device 40 by the unwinding torsionalspring (not shown).

The driving force in the direction 138 on the carrier band 120 exertedby the control cable or wire 142 (not shown) is preferably generated bya linear piezomotor, as described above, located in the control housing22. Alternatively, the force driving rotation may be generated by alinear actuator.

Where the circular track 68 acts passively, as described above, any ofthe embodiments of the circular track 68 illustrated in FIGS. 4-7 mayalternatively be used. In addition, it is not necessary that thecircular track 68 be located below the acoustic device 40 as shown inFIG. 12. It is envisioned that the circular track 68 could be locatedabove the acoustic device 40 or at any height around the outercircumference of the acoustic device 40. Furthermore, more than onecircular track 68 may be used in any of the embodiments describedherein.

In another preferred embodiment, a rotationally steerable transducerprobe is provided having two opposed multielement transducers 60, 60' asshown in FIG. 16. Two circular tracks 68 and 68' are disposed about thecircumference of the container 64. For the apparatus shown in FIG. 16,rotation of the multielement transducers 60 and 60' is effected asdescribed above with respect to the third preferred arrangement usingthe carrier band 120 connected to the sliding control cable 142.Alternatively, one or both of the circular tracks 68 and 68' may drivethe rotation of the two opposed multielement transducers in accordancewith either the first or second preferred arrangement described above.

The sliding control cable 142 passes through the gastroscope 26 in aguide tube 144. A linear piezomotor or linear actuator (not shown)contained within the control housing 22 is attached to the slidingcontrol cable 142. A torsional spring (not shown) under or around theacoustic device 40 may be used to torsionally preload the acousticdevice 40 so that the control cable 142 works against the spring'sresistance.

The acoustic fields of view 146 and 148 are indicated by phantomoutlines. Each of the multielement transducers 60 and 60' may beoptimized for typically incompatible acoustic functions, such as for twoimaging formats or two widely different operational frequencies. Themultielement transducers 60 and 60' utilize the same attenuative backingmaterial 66 and container 64. The multielement transducers 60 and 60'would typically be operated individually, although, if the operation ofthe transducers 60 and 60' is electronically interleaved andsimultaneous acoustic contact on both sides of the scanhead 36 can beachieved, the transducers 60 and 60'may be operated simultaneously toperform dual direction imaging.

Another alternative to the preferred embodiments described above isshown in FIG. 17. The multielement transducer 60 is rotated as describedabove with respect to the third preferred arrangement using the carrierband 120 connected to the control cable 142. Again, although the thirdpreferred arrangement is shown, the first or second preferredarrangements, wherein the multielement transducer is driven by acircular track 68, may alternatively be used.

Two circular tracks 68 and 68' are attached to the outer wall of thecontainer 64. In this embodiment, the attenuative backing material 66 isplaced in the container 64 above a magnetic position sensor 146. Themagnetic position sensor 146 rotates with the multielement transducer 60as both are rigidly attached to the rotating container 64. A remotetransmitter (not shown) generates magnetic fields that are detected bythe magnetic position sensor 146 attached to the container 64. Themagnetic position sensor 146 may be electrically connected in a mannersimilar to that of the electrically independent elements 130 of themultielement transducer 60, wherein flex interconnect traces 82 residenton the flexible assembly 42 and electrically conductive traces 84 on theouter surface of the container 64 are utilized. The magnetic positionsensor 146 is capable of indicating the rotational and angular positionof the transducer 60, as well as the position of the scanhead 36 withinthe patient.

The remote acoustic imaging system 32 receives real-time rotational andspatial position information so that the spatial positions of imageplanes can be recorded, or the acquisition of the image planes may betriggered at desired rotational orientations, angles or positions. Themagnetic position sensor 146 may also be used to trigger the acquisitionof multiple parallel image planes obtained as the scanhead 28 is draggedaxially along the esophagus wall with its imaging plane generallyperpendicular to the direction of dragging. During use in this mode, thedevice is not rotated as it is dragged. In these manners,three-dimensional image sets can be directly obtained using atwo-dimensional multielement transducer 60.

The container 64 and the circular tracks 68 and 68' may be fabricatedfrom a ceramic material or non-magnetic metal because the magneticposition sensor 146 may be sensitive to surrounding metallic objects.Examples of commercially available magnetic position sensor systems,which use wound coil magnetic sensors, are the Polhemus system and theAscension system.

Solid state phased-array transducers such as those described hereinimage in a plane containing the azimuthal direction of the array. Morespecifically, as shown in FIG. 2, the device shown would image the planethat includes the line 148 and the axis 48 at the particular rotationalposition shown. By rotating the acoustic device 40, as previouslydescribed, the plane being imaged would be rotated also. The mechanicalstability provided by the carrier band 120 and container 64 to the flexinterconnect traces 82 and electrically conductive traces 84, asdescribed herein, allows the acoustic device 40 to undergo rapidacceleration and deceleration without buckling, jamming, binding,fatigue and unwanted vibrations. In particular, the first preferredarrangement, wherein the carrier band 120 is laminated to the flexibleassembly 42 and the circular track 68 drives rotation, places little orno loading or contact on the flex interconnect traces 82 despite rapidmotion of the acoustic device 40.

Because the acoustic device 40, flexible assembly 42 and carrier band120 are capable of rapid acceleration and deceleration, the remotelyrotationally steerable ultrasound transducer described herein is capableof selectively and directly imaging an oblique plane. Such an obliqueimage plane may be intersected by the axis 48 but would not contain theaxis 48, as shown in FIG. 18. FIG. 18 shows, in perspective view, anoblique image plane 150 above the scanhead housing 36 of a rotationallysteerable ultrasound transducer as described herein. The axis 48 throughthe center of the multielement transducer 60 is shown intersecting theoblique image plane 150 at a point 152. A biopsy needle 154 to be imagedis illustrated in the oblique image plane 150.

To image the oblique plane 150 the multi-element transducer 60 isrotated or stepped in predetermined increments about the axis 48 over a180 degree range, after which the rotation is reversed and themultielement transducer 60 is rotated or stepped 180 degrees in theopposite direction. A selected line in the oblique image plane 150 maybe scanned at each angular position of the multielement transducer 60.

By repeating this back and forth rotation or stepping of themultielement transducer 60, sequential images of the oblique plane 150may be produced. Alternatively, the multielement transducer 60 may berotated back and forth through a range of less than 180 degrees to scanonly a portion of the oblique image plane 150. The back and forthrotation or stepping of the multielement transducer 60 is referred toherein as slewing. The frame rate of the oblique imaging is ideallylimited only by the time required for the transmitted ultrasound wavesto return to the multielement transducer 60.

Referring to FIG. 18, when the rotating multielement transducer 60 is atan angle 156, a scan line 158 on the oblique plane 150 is imaged. As thetransducer is rotated or stepped to an angle 160, a scan line 162 isimaged and, similarly, as the multielement transducer 60 is rotated orstepped to an angle 164, a scan line 168 is imaged. The ultrasoundsystem (not shown) compiles image data from each of the selected scanlines, such as lines 158, 162 and 168, and provides the image data to anoperator viewable display. The image data may be simultaneuosly oralternatively provided to a recording device (not shown).

The ultrasound system may provide the image data to the display in oneof several modes, including conventional grey scale, color doppler ordual grey scale and color doppler formats. The ultrasound system wouldbe programmed to recognize the location of the needle 154 in threedimensions, to determine the oblique plane's location, and tocontinuously provide updated oblique plane images for the near real-timeimaging of the biopsy needle 154 or other object of interest. Obliqueplane images may be interleaved with images obtained in other imagingmodalities.

It will be obvious to one skilled in the art of sonography that themethod of imaging an oblique plane, as described with respect to FIG.18, may be coupled with recently introduced software-based border andedge detection methods. For example, using the method and devicedescribed herein one may in real time, or near real time, obtain obliquesectional views of an organ or artery and perform edge detection andborder enhancement on them without having to do any image reconstructionon a work station, as would be required if all the image planes werecoaxial with the rotational axis 48 and none of them were desirablyoriented.

In this manner the remotely rotational steerable ultrasound transducerdescribed herein may be used to form a near real-time ultrasonic imageof an object in a plane that is oblique to the plane containing the axis48 of rotation for the rotatable ultrasonic multi-element transducer 60.One or more oblique image planes, such as oblique image plane 150, maybe simultaneously obtained by slewing the ultrasonic multielementtransducer 60 while scanning only those scan lines, such as 158, 162 and168, making up the oblique planes of interest. Image data issequentially extracted for sets of scan lines, such as lines 158, 162and 168 contained in the oblique plane 150, from each plane scanned bythe slewing ultrasonic multielement transducer 60. The data extractionis performed by the ultrasound system 32 software. The extracted imagedata may then be displayed in any desired manner, including display asan oblique slice.

Extremely rapid acceleration and deceleration of the multielementtransducer 60 will be limited by the mechanical inertia and naturalvibration of the flexible assembly 42 and the carrier band 120. Thus,for applications in which the multielement transducer 60 is very rapidlyaccelerated, an alternative arrangement of the flexible assembly42/carrier band 120 interface with the container 64 is shown in FIGS. 19and 20.

FIG. 19 shows an acoustic device 40 having a multielement transducer 60and two circular tracks 68 and 68', which are centered about the axis48. The multielement transducer 60 is rotated by at least one of thecircular tracks 68 and 68' as described above with reference to thefirst and second preferred arrangements.

The container 64 has been modified to include an integral bottom portion166, which has a smaller diameter than a top portion 167. By using anattenuative backing material 66 having the property of providing greaterattenuation than the material 66 as shown in FIG. 12, the shorter topportion 167 can be utilized so that the low profile of the scanheadhousing 36 is maintained. Highly attenuative yet nonrigid attenuativebacking materials 66 may be beneficially used because of the supportprovided by the container 64.

In the embodiment of FIG. 19, the flexible assembly 42 and colaminatedor nonlaminated carrier band 120 are attached to the surface 104 of thescanhead housing 36 in the region 46. Two rolling loop regions 170, 172are formed by the flexible assembly 42/carrier band 120 beneath the topportion 167 of the container 64 adjacent to the integral bottom portion166. As discussed above, the flexible assembly 42 contains flexinterconnect traces 82. Electrically conductive traces 84 are fabricatedupon or within the top portion 167 of the container 64. The traces 84preferably extend along the bottom surface of the top portion 167 of thecontainer 64 so that they may easily be connected to the flexinterconnect traces 82 of the rollable flexible assembly 42. The rollingloop regions 170, 172 of the flexible assembly 42/carrier band 120 layflat adjacent to the bottom of the top portion 167 of the container 64.

Because of the tight bending or rolling radii experienced by theflexible assembly 42 in FIGS. 19 and 20, the interconnect traces 82 mayalternatively be fine gauge coaxial controlled-impedance wires, ormultistrand or single strand noncoaxial wires. The wires are bound to adielectric insulating layer, such as KAPTON™, to form the flexibleassembly 42. The dielectric layer may have a surface metalization on itsopposite side to serve as an electrical ground reference. By laminatingthe carrier band 120 to the flexible assembly 42, the carrier band 120may alternatively serve as the electrical ground reference. Becausedrawn wires are more ductile and have greater fatigue resistance thandeposited and etched metal films, flex interconnect traces 82 fabricatedfrom the wires are capable of reliably enduring tighter bending orrolling radii.

FIG. 20 is a cut-away perspective view of the rolling loop regions 170,172 below the acoustic device 40. The rolling loop regions 170, 172 rollaround a circular path in opposed positions as the acoustic device 40rotates so that the rolling loop regions 170, 172 do not interfere witheach other. Because the rolling action axis of the rolling loop regions170, 172 changes angular orientation as the acoustic device 40 rotates,the carrier band 120 colaminated to the flexible assembly 42 may furtherimprove fatigue life.

In FIG. 20A, an alternative construction of the acoustic device 40 isprovided that allows a direct connection between the flexible assembly42, which may form the rolling loop regions 170, 172, and themultielement transducer 60. The attenuative backing material 66 isapproximately hexagonal in shape. A first flexible assembly 42 is bondedto the top of the attenuative backing material 66 with the flexinterconnect traces 82 facing upward. The first flexible assembly 42 isthen folded over one of the flat faces of the hexagonal attenuativebacking material 66. An additional fold at the bottom of the flat facemay allow the flexible assembly 42 to be routed beneath the acousticdevice 40 where an integral rolling deformable loop, such as 170 inFIGS. 19 and 20, may be formed. A second flexible assembly 42' (notshown) is bonded to the top of the attenuative backing material 66directly opposite to the first flexible assembly 42 and is folded overthe opposite flat face of the hexagonal material 66. The second flexibleassembly 42' may also be routed beneath the acoustic device 40, where anintegral rolling deformable loop, such as 172 in FIGS. 19 and 20, may beformed. The multielement transducer 60 is bonded to the top of the firstand second flexible assemblies 42, 42'. The container 64 surrounds thehexagonal faces of the attenuative backing material 66, which have theflexible assemblies 42, 42' bonded thereto.

An asymmetrical arrangement of the hexagonal attenuative backingmaterial 66, in which the flat faces of the material 66 are of slightlydiffering widths so that the individual acoustic elements 130 of themultielement transducer 60 are oriented at 30 degrees to the hexagonalface of the material 66 that contains the mating flex interconnecttraces 84, is preferred. By using the 30 degree orientation, theindividual acoustic elements 130 in one half of the multielementtransducer 60 will intersect one face of the hexagonal attenuativebacking material 66, and the remaining half of the individual acousticelements 130 will intersect the opposite face of the hexagonalattenuative backing material 66. Thus, one half of the multielementtransducer 60 may be coupled to the flexible assembly 42, and theremaining half may be coupled to the flexible assembly 42'. By havingeach half of the multielement transducer routed to a dedicated andseparate flexible assembly, electrical crosstalk between the flexinterconnect traces 82 can be substantially avoided. This isparticularly the case when the multielement transducer 60 is operated inthe continuous wave doppler mode, wherein one half of the multielementtransducer 60 transmits while the remaining half receives.

FIGS. 21 and 22 show an alternative embodiment of the rotationallysteerable transducer shown in FIGS. 19 and 20. In this embodiment, theacoustic device 40 is driven in rotation about the axis 48 by thecircular track 68 as described with respect to the first and secondpreferred arrangements. As shown in FIG. 21, the flexible assembly 42 isattached to the side wall 174 of the scanhead housing 36. The flexibleassembly 42 is connected to the integral bottom portion 166 of thecontainer 64. The electrically conductive traces 84 are routed, via topportion 167, from the multielement transducer 60 onto or into the bottomportion 166. The flex interconnect traces 82 from the flexible assembly42 are connected to the mating electrically conductive traces 84.

As shown in FIG. 22, a rolling loop region 176 is formed at the end ofthe flexible assembly 42 beneath the acoustic device 40. As the acousticdevice 40 rotates, the rolling loop region 176 rolls beneath theacoustic device 40. The phantom outline 178 of the flexible assembly 42shows the position of the flexible assembly 42 after the acoustic device40 is rotated counter-clockwise approximately 90 degrees. As discussedwith respect to FIG. 20, the fatigue life of the apparatus may beimproved by utilizing the carrier band 120 colaminated to the flexibleassembly 42 as described with respect to the first preferredarrangement.

There is no movable portion of the flexible assembly 42 in the region 46in the embodiments shown in FIGS. 19 through 22. The flexible assembly42 and the carrier band 120 are fixed to the scanhead housing 36 in theregion 46, and one or both of the circular tracks 68 and 68' driverotation of the acoustic device 40 as well as provide rotationalguidance to the acoustic device 40. Accordingly, the region 46 may beused for other functions or may be reduced in dimension to reduce theoverall size of the scanhead housing 36. Further, because the carrierband 120 does not drive the rotation of the acoustic device 40 and theflexible assembly 42 is attached to the scanhead housing 36, in theembodiments shown in FIGS. 19 through 22, the carrier band 120 is notmechanically necessary to prevent buckling, jamming and abrasion of theflexible assembly 42 except as such events may be caused by the rollingaction. The carrier band 120 may, therefore, be omitted or,alternatively, utilized for electrical and/or thermal purposes asdescribed above.

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting and that it is understood that thefollowing claims including all equivalents are intended to define thescope of the invention.

We claim:
 1. In an ultrasound probe for inspecting an interior region ofa body, the probe having a scanhead housing and a transducer array, theimprovement comprising:a magnetic position sensor located within thescanhead housing operable to provide a signal representing the spatialand rotational position of the transducer array.
 2. The invention ofclaim 1 wherein the signal is coupled to a remote ultrasonic imagingsystem that includes a mechanism for acquiring an ultrasound image whenthe transducer array is located in a predetermined position.
 3. Theinvention of claim 2 wherein the transducer array is located in apredetermined spatial position.
 4. The invention of claim 2 wherein thetransducer array is located in a predetermined rotational position. 5.The invention of claim 2 wherein the remote ultrasonic imaging systemfurther includes a mechanism for recording the position of thetransducer array.
 6. The invention of claim 1 wherein the magneticposition sensor is mounted upon a transducer array support structurehaving an ultrasonically attenuative material disposed therein.
 7. Theinvention of claim 6 wherein the support structure comprises a containerthat is rotatable.
 8. In combination with an ultrasound probe having ascanhead housing and a transducer array, a positioning systemcomprising:a magnetic field generating mechanism operable to generate amagnetic field, the magnetic field generating mechanism being locatedoutside the scanhead housing; and a magnetic position sensor locatedwithin the scanhead housing, the magnetic position sensor operable todetect the magnetic field and provide a signal representing the spatialand rotational position of the transducer array with respect to themagnetic field generating mechanism.
 9. The invention of claim 8 whereinthe signal is coupled to a remote ultrasonic imaging system thatincludes a mechanism for acquiring an ultrasound image when thetransducer array is located in a predetermined position.
 10. Theinvention of claim 9 wherein the transducer array is located in apredetermined spatial position.
 11. The invention of claim 9 wherein thetransducer array is located in a predetermined rotational position. 12.The invention of claim 9 wherein the remote ultrasonic imaging systemfurther includes a mechanism for recording the position of thetransducer.
 13. The invention of claim 8 wherein the magnetic positionsensor is mounted upon a transducer support structure having anultrasonically attenuative material disposed therein.
 14. The inventionof claim 13 wherein the support structure comprises a container that isrotatable.
 15. A method of determining a position of an ultrasound probecontaining a transducer array, the method comprising the stepsof:providing a magnetic position sensor attached to the probe, themagnetic position sensor operable to provide a signal indicative of thespatial and rotational position of the transducer array; generating amagnetic field from a position outside the probe; locating the magneticposition sensor within the magnetic field; and receiving a signal fromthe magnetic position sensor representing the spatial and rotationalposition of the transducer array.
 16. The invention of claim 15 furthercomprising the step of acquiring an image when the magnetic positionsensor reaches a predetermined position.
 17. The invention of claim 16wherein the step of acquiring an image is at a predetermined spatialposition.
 18. The invention of claim 17 wherein the step of acquiring animage is repeated at a plurality of predetermined spatial positions. 19.The invention of claim 15 wherein the transducer array is mounted torotate within the probe to a plurality of rotational positions, and themagnetic position sensor is mounted to rotate with the transducer array.20. The invention of claim 19 further comprising the step of acquiringan image when the transducer reaches a predetermined rotationalposition.